R script to compare data

I need an R script that reads / compares / exports results from 2 Excel files.

Script needs to:
1. Read 2 Excel file with 1 Sheet
2. Excel file will have X number of attribute columns and Y number of value (numerical) columns
3. Create a Key using the attribute columns in each file by concatenating values in attribute columns e.g. Key = ValueA2-VaueB2-ValueC2-ValueD2 etc.
4. I need to be able to change file names / column names myself
5. Using this key match rows in 2 Excel files and compare value (numerical) columns for each row of data
6. Script needs to handle comparison of 0 to 0 and nulls to null values
7. Volume of data approx.. 200-500k rows

Use of any library possible as long as script contains commands to install them.

Example attached.